Choosing the type of flow regime in HEC-RAS for FEMA studies 1

[biker317]

I have reviewed projects done for FEMA, mapping the 100 and 500 year studies by different contractors. I have seen models turned in been run with 'Supercritical' flow regime and 'Mixed' flow regime. So my 2 questions are:

1) Does FEMA guides and specs favor any time of run? I do not recollect anything mentioned about this.
2) How do the results (the WSEL) vary for the 3 flow regimes?

thanks

 

[cvg]

If you have

subcritical channel - then run in subcritical regime
supercritical channel - then run in supercritical regime
for a channel that switches back and forth - use mixed flow

If you aren't sure, then try mixed flow regime. then after running it, you determine it is not mixed, switch to one of the other modes as appropriate.